The present invention relates in general to a control panel for controlling conditions of a process plant, and more specifically to a system for positioning and operating the control devices of the control panel relative to the display and monitoring devices.
Annunciator systems have been developed for monitoring and displaying operating conditions in complex process plant systems. The typical annunciator system might include a plurality of gages for indicating variable parameters such as pressures, temperatures quantities, or the like for illustrating the various conditions in the process plant. When a complex process is displayed by an annunciator system, the various details and indicators may be so many in number and so complex in their arrangement that a graphic display is desirable in order for the plant operators to understand and easily read the various indicators. A graphic display of this type might include a translucent panel positioned in or near the annunciator cabinet which carries symbols that represent pumps, valves, liquid levels, pressures, and other plant equipment and conditions, and flow lines extending between the various symbols. The various symbols on the display panel are illuminated by lamps placed behind the display panel, and the light emitted from the lamps would represent various plant conditions. For instance, when a lamp illuminates the symbol of a pump on the display panel, it would indicate a certain condition existing in a corresponding pump in the process plant; e.g., if the pump were in operation, overheated, or not operating properly. Similarly, a lamp might be utilized to illuminate the symbol of a storage tank to indicate an empty, properly filled, or an overfilled condition in the storage tank. Associated with such annunciator systems are control systems by which the process plant can be controlled in response to the conditions indicated by the annunciator display and monitoring operations.
Often times, the control system includes a separate array of switches or other control devices disassociated from the graphic display of the annunciator system. That is, the switches are arranged on a separate control panel located at some point removed from the graphic display. Certain of the symbols on the graphic display may correspond with certain of the switches of the switching panel. When the operator desires to control a condition within the process plant which is indicated by a certain symbol on the graphic display, the operator must search out the corresponding switch on the control panel in order to actuate the indicated condition. In such control systems with switches disassociated from the graphic display, precious seconds can be wasted in properly relating the graphic display symbol or function and the corresponding switch. Once a symbol on the graphic display is lit up, for example, the operator must search the separate control panel for the appropriate corresponding switch. Furthermore, the separate control panel and graphic display set in a control room occupy a great deal of space, much of which could be conserved if the separate control panel was eliminated.
Other control systems include switches which are mounted directly onto and protrude from the graphic display of the annunciator system, in locations which coincide with the symbolic representation of the process or condition that is controlled by each such switch. One practice is to bore a hole through the graphic display panel and attach, extending therethrough, a button or toggle switch or similar type switch. The switch protrudes from the display adjacent the corresponding symbol or sometimes replaces the symbol itself. In such control systems with switches mounted directly to the graphic display panel, the ability to vary the process plant display (or flow chart) is very limited and costly. Each time the operational process of the plant is to be varied, e.g., a pump moved or valve sequence rearranged, a new display panel must be constructed or else new holes must be bored and old holes plugged in the existing panel.
Examples of typeical graphic display annunciator systems and related control devices of the prior art are shown by way of example in U.S. Pat. Nos. 3,624,648 to Willoughby, and 3,754,245 to Peprnik.